Gears are widely used in all sectors of mechanical engineering to transmit movements, from watch making up to the heavy industry, transportation and automotive (gearbox, gear pump, etc.). These gears must have a suitable and constant quality. Therefore, the toothed wheels, the toothed pinions, the toothed shafts or similar must be checked individually after machining on the production lines. In the rest of the text, the general term of “part(s)” shall be used to include all parts that can be used in a gear, a pinion/rack transmission or similar.
The classical solution consists in checking these parts after manufacture either manually or in a metrology department, on coordinate measuring machines. However, this solution is inappropriate today for the following reasons: it is a discontinuous checking process, carried out in static mode, which requires a relatively long checking time and generates a delay that is detrimental on the production line when an intervention is necessary on the cutting machine to correct the detected defects, leading to significant waste that impacts negatively the manufacturing cost of these parts.
It is therefore desirable to use automatic checking machines that are able to check continuously, in dynamic mode, in an accurate, reproducible and fast way the features of the teeth of these parts, directly on the manufacturing line, thus allowing to control almost in real time the cutting machine in order to reduce the waste as much as possible and to optimize the manufacturing costs.
The check implies necessarily the inspection of the various characteristics of the teeth of a part, preferably in operation, that is to say in dynamic mode. The check must allow detecting radial deviations linked with the radial composite deviation F″i (run-out), with the radial jump f″i (teeth jump) and with the center distance, as well as the angular deviations linked with the helix deviation and with the cone inclination deviation. During the check of the teeth, one also tries to check the part for shocks it might have suffered during handling. In operation, these shocks generate vibrations that can be detected, in particular by an acoustic check.
Machines that tend to meet the need for dynamic checking of teeth already exist, but they are not totally satisfactory. These machines generally include a precision spindle equipped with an expanding arbor that centers, clamps and rotates the part to be checked, and two master pinions used for measurement and located on either side of the part to be checked: a first master pinion that meshes without play with the part to be checked, in contact on both two-flanks, used for checking the radial composite deviations, and a second master pinion mounted on a holder that swivels in the inclination (cone) and deviation (helix) planes, this pinion being stepped so as to provide only two contact areas located at the two ends of the functional width of the teeth to be checked, this second gear being used for checking the helix and cone deviations. An example of a dynamic check of angular deviations using a stepped pinion is described in publication U.S. Pat. No. 7,775,101 and an example of a check of radial deviations is described in publication US 2006/0254055.
Nevertheless, these checking machines are particularly onerous. This is all the more true when several master pinions must be provided so as to check a wide diversity of parts in production. The master pinions must be adapted to every module and every tooth height of the parts.
The swiveling mounting of the stepped gear for checking the helix angle and the cone angle poses a problem of inertia that has to be overcome to remain in contact with the teeth and to follow the helix and cone deviations during the dynamic mode measurement. Therefore the rotational speeds must be reduced, which slows down the checking cycle. Furthermore, the friction at teeth level can distort the measurement.
The approximation of the obtained result that is inherent to the two-flank measurement method with the stepped master pinion is also a major disadvantage. This is a measurement that gives an average value of the inclination deviation of the helices of both tooth flanks and that limits itself to the detection of the two defects, combined or not, of tooth conicity and inclination, hence misinterpretations. Said defects are not individualized and cannot be quantified separately. So, probably good wheels may be scrapped and conversely. Likewise, these approximative results do not allow to act accurately upon the cutting machine to correct the detected defects.
Furthermore, with this measurement method, the consecutive and simultaneous contact of the stepped master pinion and of the part to be checked on several teeth at the same time due to the covering effect of the helical toothing and to the inclination of the generating lines on the flanks does not allow reading other defects due to a faulty positioning of the part on the cutting machine.
In addition, the differentiation between the two flanks of the teeth by reversing the direction of rotation is not guaranteed. Only a check of the composite tangential deviations by meshing on one flank carried out at the level of the nominal diameter of the toothing and then on the other flank would allow a differentiated measurement.
Finally, the master pinions of these checking machines work without play, which does not correspond to the normal operating conditions of the gear. Indeed, the results obtained are not representative of reality.